Backplate latch mechanism for machine guns



Dec. 7, 1943. s. G. GREEN 2,335,854v

BACK PLATE LATCH MECHANISM FQR MACHINE GUNS Filed Aug. 22, 1940 Fig.5-

x Z! Z/ INVENTOR Samuel B- ElYE an ATTORN EY Patented Dec. 7, 1943 BACKPLATE LATCH MECHANISM Fort MACHINE. GUNS Samuel G. Green, Gray, Ga. Application August 22, 1940, Serial No. 353,588,

4 Claims. ('01. 89-1 (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a latch mechanism particularly adapted for use in securing the back plate of a machine gun of the Browning type in its assembled relation on the receiver and constitutes an improvement upon my U. S. Patent No. 2,108,060 issued Feb. 15, 1938.

In view of the increased cyclic rates of machine guns of the Browning type and the increased inertia forces developed incidental to these increased cyclic rates, along with the fact that the back plate in the modern gun is not held in assembled relation on the receiver by the driving spring rod, it has become essential to positively ensure locking of the back plate to the receiver by suitable means unailected by inertia forces and of such a character as have little probability of being accidentally unlatch'ed Also in the interest of economy it is desirable that latch means of the above character Will entail little or no modification of the existing type of back plate.

While the latch hitherto proposed in the patent above referred to is satisfactory, the latch of the present invention is an improvement; in that, all parts are secured to the back plate without modification of the latter while the locking member has been arranged to have a translatory motion transversely of the line of travel of the internal gun and is, therefore, not subjected to an unlocking force arising from the forces of inertia. Also through arranging the locking member to be translated to its locking and unlocking positions of the latch, while retaining a pivoted latch, the probability factor in regard to accidentally obtaining simultaneously the combined motions required to render the latch mechanism inoperative has been greatly reduced although equal or improved facility of' designed unlocking of the locking member and unlatchirig of the latch member is retained.

The specific nature of the invention as wellas other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which: 7

Fig. 1 is a fragmentary elevational view partially in section of the rear end portion of the right hand side of the receiver of a-machine gun of the Browning type with the back plate shown in section to show the manner in which the latch mechanism of this invention, also shown in sec-'v tion, is secured to the back plate;

Fig. 2 is a section taken upon the line 2-2 of Fig.1 to show the Vertical'sliding relation of the.

back plate and receiver side plates,. common to machine guns of the Browning type;

Fig. 3 is a; rear elevation of the back plat showing the latch mechanism of the invention secured thereon in partial section to better disclose a certain detail;

Fig. 4 is a side elevation of the back plate and attached latch mechanism taken from the left of Fig. 3.

Referring now to the drawing by characters of reference, there is shown in Figs. 1 and 2 the rear end portion of a receiver, generally 'indi'-- cated at NJ, as provided in machine guns of the Browning type.

14, respectively. secured to each other to provide a hollow structure of rectangular section as shown. The rear end portions of side plates [2 and M are formed to provide guide elements. l5'

extending longitudinally thereof for a purpose. to be presently made apparent;

The rear end of the receiver is normally closed by a back plate I6 formed with forwardly pro-- Provision is made to limit sliding movement of the back plate on the side plates in a direction toward closing relation with respect to the rear end of the receiver by slightly projecting the bottom plate l3 outwardly beyond the rear ends-of the side plates l2 and It as indicated at 19, in order to form a seat upon which the back plate may abut to be arrested in closing relation tothe rear end of the receiver also as well known.

A common example of a back plate of the Browning type is formed to centrally carry a buffer tube 20 as shown in Figs. 1 and 2, and adjacent its opposed-transverse edges is-provided with; outwardly projecting ribs parallel thereto, or similar projections 21 which serve on a'gun that is flexibly mounted to support the upper and lower hand grip bars, respectively; such as the bars 15 and I3 shown in Fig. 2 of my prior patent. above referred to. Further, in the flexibly mounted gun'the back plate is transversely ma- The receiver l comprises top,v right, bottom and left side plates ll, l2, l3 andv The back place is secured to chined just below the buffer tube, as indicated at 22 to form a seat for a trigger supporting bracket 23 comprising rearwardly projecting lengthwise spaced aligned ears 24 carried by a web portion 25 secured upon the seat as by the fastening means 26 extending through the web and back plate. Further the back plate is upwardly slotted from its lower edge to provide for mounting a latch 21 therein by means of a pin 28 and a bored boss 29 is formed integral with the back plate to provide a bearing for a hollow plunger 30. A spring 3| is disposed within the plunger and is normally seated upon the arm of a trigger mounted in the trigger supporting bracket 23 acting to urge the trigger to non-firing position and the plunger into engagement with the finger 32 of the latch to bias the latter into a position where the toe 33 thereof abuts the inner surface of the back plate in which position the nose 34 is adapted to engage projection I9 in interlocking relation.

In those instances where back plates following the example above illustrated are used in a flexibly mounted gun means similar to the locking means 26 shown in Figs. 1 to 6 of the cited patent may be expeditiously employed for locking the latch. 21 in latched relation with the projection IQ of bottom plate l3 owing to the facility with which such securing means may be mounted on the lower hand grip bar 16. Similarly in those cases where the buffer assembly is vertically mounted on the back plate securin means such as 34 shown in Figs. 7 and 8 of the patent may b used.

However, when a back plate of the type herein disclosed is employed with a gun mounted on a fixed mount; for example, an airplane mount wherein synchronizing gear is employed to actuate the trigger, the hand grip bars [5-46 of the cited patent are eliminated as well as the trigger normally mounted in the trigger supporting bracket 23, consequently a problem is presented in providing means for securing the latch 2'! in latching relation to the bottom plate which may be rendered inoperable by a natural preceding incidental motion of the hand or fingers utilized in unlatching latch 21; positive in action to secure the latch in latched relation to the bottom plate when subjected to inertia forces during firing; and possessing a high safety factor against being rendered inoperative accidentally, without modification of the back plate.

By this invention latch securing or locking means conforming with the above stated requisites have been provided. As shown in the drawing a locking member 35 comprising a body portion 36 having spaced projections 31 extending above its upper edge is mounted upon the trigger bracket 23 with the projections 31 disposed outside of the ears 24 by means of a pin 38 passing through aligned apertures of the ears and projections. The projections 31 of the locking member are spaced a greater distance apart than the ears 24 of the trigger supporting bracket 23 and resilient means, such as a helical spring 39,

is interposed between theconfronting faces of the leftmost ear 24 and projection 31 to normally retain the confronting faces of the rightmost ear 24 and projection 3'! in abutting relation as viewed in Fig. 3. The projections 3'! are arranged to extend inwardly toward the back plate to points where they clear the seat 22 formed thereon by small tolerances when the body portion 36 of the locking member is disposed in' parallelism with the back plate; whereby the locking member is constrained to translatory motion transversely of the line of reciprocation of the internal gun and thereby not movable to an unlocking position by the forces of inertia set up by the gun in firing. As shown more particularly in Fig. 3 the body portion 36 of the looking member 35 is recessed as indicated at 49 in a manner that when the locking member occupies its normal locking position shown in Fig. 3 a substantial part of the body portion to the right of the recess Will be disposed above the latch finger 32 in such spaced relation as to prevent upward pivotal movement of the latch to unlatched position. By manually translating the locking member 35 to the right by the thumb while simultaneously exerting an upward pressure on the latch finger 32 with the index finger the recess 46 may be positioned directly over the latch finger 32 during the interval that the latch finger is traveling through a distance corresponding to the clearance between the latch finger and body portion of the locking member whereafter the latch may continue to be pivoted to a position with its finger 32 disposed in recess 40 of the locking member to disengage the nose 34 thereof from' the projection E9 of bottom plate I3. This motion of the locking member and latch member as will be observed, may be ef fected by a single hand of the operator in a smooth, continuous, natural movement.

While the latch mechanism comprising this invention has been developed as a result of the requirements of a fixedly mounted gun provided with a back plate of the example herein illustrated, it may and will preferably be employed on all types of mounts owing to the advantage of interchangeability gained by the standardization of parts thereby. .In the fixed gun the only additional part required in this latch mechanism is the spacer 42 mounted between the ears 24 of trigger supporting bracket to provide a seat for, the upper end of spring while in the flexibly mounted gun no additional part is required since the trigger mounted between the ears 24 serves as a seat for the spring 39.

In brief, standardization may effected on all types of mounts with this latch mechanism whereas standardization is limited to certain types of mounts by the latch mechanism or" the patent referred to, aside from the question of the improved probability factor in regard to accidental unlatching of the present latch mechanism.

Having now described a present preferred embodiment of the invention I claim:

1. A back plate of the type adapted to be slideably mounted upon the receiver of a gun to close an end of the receiver comprising a latch mounted on the back plate and provided with a rearwardly extending finger portion, means for normally urging the latch to downward l cking po sition, alocking member provided with a downwardly projecting portion, means mounting said locking member for sliding movement transversely to the direction of mounting of the latch, and means normally urging the locking member bodily laterally to bring said projecting portion into the path of the upward movement of the finger portion to prevent unlocking movement of said finger portion, said urging means being arranged to be overcome by a manual movement of said locking member to clear the path of the finger portion of the latch for an unlocking movement, the relation of the locking means and the finger portion of the latch being such that the manipulation of both may be effected by a single hand of the operator in a smooth, continuous natural movement.

2. A back plate of the type adapted to be slideably mounted upon the receiver of a gun to close the end of the receiver comprising a latch pivotally mounted on the back plate provided with a rearwardly extending finger portion, a bracket secured to the back plate, a pin mounted on the bracket with its axis disposed parallel to the pivotal axis of said latch, a locking member having a projecting body portion slidably mounted on said pin adapted to be positioned with the projecting body portion thereof in blocking relation to pivotal unlocking movement of said latch, and means operative to normally maintain the looking member with its projection in said blocking relation to pivotal unlocking movement of the latch.

3. The structure of claim 2 including means interposed between said bracket and latch for normally urging the latch into relative latching relation.

4. A back plate of the type adapted to be slidably mounted upon the receiver of a gun to close an end of the receiver, a latch provided with a finger piece and latching nose pivotally mounted adjacent the lower transverse edge of the plate with the finger piece extending rearwardly and the nose extending downwardly for pivotal movement in a plane normal to said transverse edge, abutment means on said latch adapted to abut the back plate for limiting downward pivotal movement of the latch, said back plate being formed with a transverse seat above the latch, a trigger supporting bracket provided with spaced ears secured on said seat with the ears in transverse alignment, a pin mounted on said ears, a locking member comprising a body portion provided with upwardly extending projections spaced a greater distance apart than said ears slidably mounted on the pin with its projections in a1ignment with and outside of the ears, said projec tions cooperating with the transverse seat to maintain the body portion in substantial parallelism with the back plate overlying the locking member, resilient means interposed between the confronting faces of the leftmost ear and projection for normally retaining the confronting faces of the rightmost ear and projection in abutment, said body portion of the locking member depending in close proximity to the finger piece of the latch to prevent upward pivotal movement thereof to an unlatched position when in normal position and being formed with a recess adapted to register with the finger piece when translated to the'right, a bored boss on the back plate intermediate the latch and locking member, a hollow plunger mounted in the bore of the boss engaging the latch, spring seat means mounted on the pin intermediate said ears, and a spring mounted in said hollow plunger engaging the spring seat means urging said abutment means into engagement with the back plate.

SAMUEL G. GREEN. 

